Planar Hall effect and Anisotropic Magnetoresistance in Thin Films of Chiral Antiferromagnet Mn3Sn

Abstract

Antiferromagnetic Weyl semimetals with spin chirality offer excellent platforms to address the Berry phase physics, which manifests prominently in several of their electro-optical and electro-magnetic responses including as a large anomalous Hall effect (AHE) and spin Hall conductivity. Here, we report measurements of magneto-transport in c-axis textured Mn3Sn thin films grown on the [111] plane of single crystal MgO. At room temperature, these films display a weak uncompensated magnetic moment of \approx 0.12 \micro_{B}/f.u. in the basal plane and a longitudinal resistivity (\rho_{xx}) close to \approx 3.8 \micro\Omega.m. A residual resistivity ration (\rho_{xx} (300 K)/\rho_{xx} (2 K)) of \approx 3.92 further indicates the high quality of the films. While at 300 K a weak AHE together with field-linear Hall resistivity (\rho_{xy}) is observed in magnetic fields (H) applied perpendicular to the Kagome planes, the temperature (T) dependence of \rho_{xy} shows prominent signatures of three magnetic phases in the temperature regime of 2 to 300 K. The \rho_{xy} also derives a non-trivial topological contribution (\r{ho}THE \approx 1n\Omega.m) in the spin glass phase which appears at T \geq 100 K. Our measurements of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) over a wide H-T phase space reveal the hitherto unseen effects in the three magnetic phases of Mn3Sn. While the AMR and PHE are negative in the inverse triangular spin phase (250 K \geq T \geq TN), the helical phase (100 \geq T \geq 250 K) is devoid of anisotropic in-plane resistivity, and the spin glass phase shows a sign reversal of AMR with the increasing magnetic field. The origin of this sign change in AMR/PHE is attributed to the emergence of topologically protected spin textures like skyrmions where the fictitious effective magnetic field is estimated to be \approx 4.4 tesla.